1. Field of the Invention
The invention covers the addition of novel sensitizers to positive photoresists to increase their sensitivity to light. This invention has particular application in, but is not limited to, the formation of printing surfaces, formed by a flash exposure process.
2. Discussion of the Prior Art
A positive photoresist is an organic material, which when exposed to radiation, undergoes chemical reactions which result in an increased solubility of the exposed material.
Quinone diazides provide a useful mechanism in achieving a solubility difference between exposed and unexposed portions of a photoresist. The reaction sequence is believed to be as follows: ##STR1##
Thus, the portion of the quinone diazide photoresist exposed to radiation will have increased solubility to an alkaline solution.
Therefore, such coatings have potential utility in forming photo-resists for metal plating and for the etching of metal plates, ceramics or the like in a pattern for the manufacture of printed circuits and printing plates.
In the production of printing plates the photoresist composition is coated on a support such as a metal plate or foil, e.g., aluminum or zinc. After drying, the plate is exposed under a positive or negative master to the action of radiation and is then developed. Development in an alkaline solution will cause removal of the portion exposed to radiation.
With exposure through a positive master and alkaline development, the finished plate has a raised portion conforming to the desired image. When the printing plate is inked with a greasy ink, the ink adheres to the raised portions of the plate which are formed by the remaining unexposed photoresist. From this plate can then be obtained positive copies corresponding to the positive master. Alternatively, the plate can be etched with the subsequent removal of the photoresist.
With exposure through a negative master, the exposed photoresist is removed with an alkaline solution and the plate can then be plated with the photoresist acting as a plating mask. Subsequently, the photoresist is removed to give a printing plate.
These processes have been described in U.S. Pat. Nos. 3,046,118, 3,106,465, 3,148,983 and 3,402,044.
Compounds containing two or more nitrogen atoms, at least one of which is bonded to a hydrogen atom, are disclosed in U.S. Pat. No. 3,661,582 as additives to increase the sensitivity of quinone diazide photoresists.